Method of removing sealant from fuel tanks



1953 K. R. WH|TCOMB ETAL 2a653,116

METHOD OF REMOVING SEALANTFROM FiJEL' TANKS Filed March 16. 1949 v SnicntorS KEITH/Z WHITCOMB v EUGENE E. F/NCH attorney larly the joints ofthese fabricated tanks.

Patented Sept. 22, 1953 METHOD OF REMOVING SEALANT FROM FUEL TANKS Keith R. Whitcomb and Eugene E. Finch, Los Angeles, Calif., assignors to Gee-Bee Chemical 00., Inc., Los Angeles, Calif., a corporation of California Application March 16, 1949, Serial No. 81,824

8 Claims.

This invention relates to a method and apparatus for removing the sealant that lines the interiors of integral fuel tanksparticularly of aircraft.

Modern airplanes, more particularly those requiring large fuel capacity, employ certain spaces between wing ribs for storing fuel. These spaces,

called integral tanks, have many obstructions and projections and are of indeterminate size and shape. Consequently, a compound is used to line or coat the interior surfaces of such-tanks so they may efficiently carry highly volatile fuel without leakage thereof. These compounds, which are termed sealants in the present art, vary in composition, examples being zinc chromate paste, accelerator-cured Thiokol, water dispersion Thiokol and Buna N synthetic rubber. These, or like compounds, are applied to coat and, therefore, seal integral tanks and more particu- The thickness of the coating varies from as little as one-sixteenth of an inch to as much as one and one-half inches or more.

The effective life of such a sealant varies, but after some eight thousand flying hours, the same has usually spent its useful life and is no longer considered safe to hold fuel without leaking and requires removal and replacement by a fresh coat.

At the present time, two methods are used for effecting removal of inefficient sealant-the spray-on method and the fill-and-drain method.

Both methods for de-coating the tanks of a large passenger or cargo airplane and for re-coating the same are quite expensive, the cost, at this writing, being between thirty and forty thousand dollars. The first of these methods requires some one thousand man-hours of time and the use of two hundred and fifty gallons of a suitable base material at several dollars per gallon.

The other method, while requiring only three hundred man-hours of time, results in the unrecovered loss of some one hundred and fifty gallons of the expensive base material and requires a minimum working volume of approximately 1500 gallons.

It will be evident that a large proportion of the cost of re-lining integral tanks results from the present inefficient methods of removing the old coating.

Also, in the spray-on method, the time of several men, expensively accoutered to protect them from harmful fumes and liquids, is necessary for first spraying on the walls of the tanks several coats of stripping material and then scraping off the partially dissolved coating. This task is of such hazardous nature that high compensation is demanded therefor. This method is also time-consuming and results in further loss because the airplane is grounded an inordinately long time during the coating removal and replacement period.

The fill-and-drain method has a disadvantage in that a large volume of solvent material is required to fill the tanks, and the additional fault that some sixteen to forty-eight hours of soaking is required before the coating is removed by manual scraping, the men also working in a dangerous environment.

According to the present invention, the here inafter described method of removing sealant from integral tanks, comparable in size to the examples above given, entails time comparable to that given for the fill-and-drain method and a minimum working volume of solvent and with less attending loss of the latter. Further, said novel method is carried out with the tanks sealed off, except for a suitable pressure-relief vent, and the operators are not subjected to the hazards attending close proximity to the solvent or the fumes thereof.

The primary object of the invention, therefore, is to provide a novel and improved method for removing the sealant of integral tanks that is efiicient; safe, effective, and saving of both cost and time over previous methods.

Another, object of the invention is to provide novel and improved apparatus that is adapted for operative association with the integral tanks of airplanes for setting up a continuous recirculating spray fiow of solvent into and out of such tanks to remove the sealant without the need of scraping the same from the walls of the tanks.

The invention also has for its objects to provide such means that are positive in operations, convenient in use, easily installed in a working position and easily disconnected therefrom, economical of manufacture, relatively simple, and of general superiority and serviceability.

The invention also comprises novel details of construction and novel combinations and arrangements of parts, which will more fully appear in the course of the following description. However, the drawings merely show and the following description merely describes one embodiment of the present invention, which is given by way of illustration or example only.

In the drawings, like reference characters designate similar parts in the several views.

Fig. 1 is an elevational view, partly in section of apparatus according to the present invention and shown operatively connected to integral tanks of an airplane to remove the sealant from the walls of said tanks.

Fig. 2 is an enlarged cross-sectional view taken -on line 22 of Fig. 1..

In the drawing, a portion ofthe wing of an 20 is then applied to connect the spray head and fitting 2lon panel N. This panel is then firmly secured .in place to close the access opening in said tank. Connections 22 and 23 are then fitted in place and the apparatus is ready to function.

The pump is then started to force a stripper or solvent from receptacle it through the orifices airplane is shown in section to reveal that the same is divided into compartments 5, i and I, by means of transverse walls or bulkheads 2. One or more of said compartments may comprise an integral tank. In this disclosureand in the appended claims the term integral tank" is intended to designate one of said compartments or two or more adjacent compartments that are in intercommunicationas by openings 0 in bulk- The apparatus that is illustrated comprises,

generally, a truck I5, a solvent storage receptacle IS, a pump I1 and a unit l8 for driving said pump, all mounted on said truck, a manifold spray head [9 adapted to be disposed within an integral tank, an articulated flow connection between the spray head I9 and a fitting 2| extending through panel H), a fiow connection 22 from the pump I! to said fitting, and a flow connection 23 from the tank to the solvent storage receptacle l6.

The truck is wheel-mounted so that the present apparatus is portable and readily positioned for operative connection to an integral tank.

or perforations of the spray head to spray desired portions of the inner surfaces of the tank.'

The solvent and the dissolved or dispersed coatin'g material will then flow downward from the side walls of the tank, collect on the bottom thereof, and fiow along said normally sloping bottom into connection 23 and thence back in receptacle it. Thus. a continuous circulation of stripper or solvent is established that acts on the sealant coating the tank.

After a suitable period of re-circulation, two

2 preferred, but alternate methods may be em- The receptacle I6 is of suitable capacity to.

insure a constant fiow of solvent therefrom, under pressure of pump Il, through flow connection 22 and 20, to spray head l9. Said receptacle may be provided with a screen-24 or like means for collecting material dispersed by the solvent and yet permitting drainage therethrough of the solvent for re-circulation by the pump. Any residual particles of said material that may pass through screen 24 may be inter.- cepted byone or more screens 25 to insure that uncontaminated solvent is pumped to spray the integral tank.

The spray head [9 may be variously made. As shown, the same comprises coupled lengths of tubes or pipes 26 to provide the spray head with a length suitable to the length of the tank to be sprayed thereby. The articulated connection 20 may also vary, the same being shown as comprising lengths of tube or pipe connected by swivel flow joints... Connection 20 is preferably imperforate. The spray head sections 26, however, are provided with a multiplicity of perforations 21 that are so arranged that fluid passing there through is'directed toward the top wall of the integral tank and at least the upper portions of the side walls thereof, although, if desired, perforations may be provided for spraying downward also.

In use, the spray head I! is made up and then introduced into the integral tank. Clips or other tie means 20 may be employed to connect said spray head to bulkheads 8 or to any. convenient points of the tank. The articulated connection ployed for thoroughly ridding the walls of the tanks of residual sealant. In one case, the door l0 may be left in place to keep the tank sealed and, thereby, reduce the tendency of the solvent material to evaporate and form a hardened water-insoluble deposit on the walls of the tank. While theinterior of the tank is thus kept in a moistened state, either through connection 2| or through pump l1, an emulsifying liquid is introduced to render the solvent-sealant solution in' the tank water-'rinsable. Subsequently, high pressure hot or cold water may be employed for rinsing outthe emulsified solution.

In the other case, door I0 is removed to open the tank to atmosphere. The solvent in the solvent-sealant solution, being highly volatile, rapidly evaporates, resulting in the forming of a hardened or tacky water-insoluble film or deposit on the tank walls. This film is then removed by the introduction, in spray form, of a thickened, water-rinsable, slowly evaporating stripper which restores the film to its initial solvent solution. Finally, high pressure hot or cold water is employed to obtain final rinsing.

The above defined alternative methods may have the various steps thereof combined. For instance, the solvent and the water-rinsable stripper may be simultaneously applied, etc.

For certain solvents or strippers, heating may be desired. Accordingly, a suitable heater 29 may be used to heat container [6, or connection 22 or fitting 2| may embody heating means.

Whereas an indeterminate but great length of time is needed to remove the coating of a tank by the hand spray and scrape method, and

some sixteen to forty-eight hours of soaking are necessary for the fill-and-drain method to be effective followed by some handwork and a high pressure (300-400 lbs/sq. in.) warm (120 F.) water rinse, only some two to eight hours of continous spraying at 30-90 lbs/sq. in. at 60 to 120 F. temperature followed by a high pressure (300- 400 lbs/sq. in.) warm (120 F.) water rinse according to the present method, is needed for removing the coating of an integral tank.

Moreover, the entire method is carried out in a safe manner, no person being subjected to the fumes of the highly volatile solvent since the apparatus is necessary, merely to insure that the same is functioning properly. Thus, one attendant may control the operation of several such devices in simultaneous operation.

While the invention that has been illustrated and described is now regarded as the preferred embodiment, the construction is, of course, subject to modifications without departing from the spirit and scope of the invention. It is therefore not desired to restrict the invention to the particular form of construction illustrated and described, but to cover all modifications that may fall within the scope of the appended claims.

Having thus described our invention, what we claim and desire to be secured by Letters Patentis:

1. The method of removing the sealant from an aircraft integral fuel tank that comprises impinging a spray of volatile solvent against at least the upper portions of the sealant of the tank while the latter is sealed, simultaneously gravitationally draining free solvent from the tank with removed sealant material, applying a waterrinsable, emulsifying spray to the sealant, and then applying water under higher pressure to rinse free solvent and emulsifier, and removed sealant material, from the tank.

2. The method of removing the sealant from an aircraft integral fuel tank that comprises impinging a spray of volatile solvent against at least the upper portions of the sealant of the tank, simultaneously gravitationally draining free solvent from the tank with'removed sealant material, rendering the solvent water-rinsable by applying a substantially less volatile, waterrinsable, solvent-miscible spray to the solvent on the sealant, and then applyingv water under substantially higher pressure than either spray to rinse free liquid of both sprayings, and removed sealant material, from the tank.

3. In the method of removing th sealant from an aircraft integral fuel tank, the steps of impinging a high pressure spray of volatile solvent for approximately two to eight, hours against at least the upper portions of the sealant of the tank, the spray being effected by a pressure of approximately thirty to ninety pounds per square inch and the spray material being of a tempera-- ture within the range of F. to 120 F., simultaneously gravitationally draining free solvent from the tank with removed sealant material, rendering the solvent water-rinsable by applying a substantially less volatile, ,water-rinsable, solvent-miscible spray to the solvent on thesealant, and then applying water under relatively higher pressure than the solvent spray and at least approximately 300 pounds per squar inch.

4. The method of removing the sealant from within a multiple-cell, integral fuel-tank of an aircraft that is divided by at least one bulkhead, which comprises a continuous closed-circuit proc-- ess of impinging a spray of volatile solvent against sealant in the cells and upon opposite sides of the bulkhead, thus removing sealant and forming a flow of solvent carrying sealant, draining the mixture of solvent and its carried sealant material by gravitation from one cell to another.

'draining said mixture gravitationally from the latter cell to remove same from the tank to a place below the tank, passing the mixture through a screening means thereby substantially removing the transported pieces of the sealant from the solvent and returning the residual solvent under pressure to the tank to be used again as a spray.

5. The method of removing the sealant from within an aircraft integral fuel-tank, which comprises impinging a spray of solvent against the sealant to remove same, washing free sealant from the tank by free solvent, screening out sealant from the solvent, re-circulating the latter as a spray against remaining sealant, and, when the sealant is substantially removed, applying rinse Water to remove solvent and loosened sealant remainting in the tank.

6. The method of removing the sealant from Within an aircraft integral fuel-tank, which comprises impinging a spray of solvent against the sealant, thereby removing portions of the sealant and. also loosening other sealant, removing the free solvent and its accompanying sealant material from the tank, screening out sealant from the solvent, re-circulating the latter as a spray against remaining sealant, and then applying water under substantially higher pressure to rinse solvent therefrom and to remove further portions of the sealant that are loosened but not removed by the solvent spray, anddraining the water, loosened sealant and solvent from the tank.

'7. The method according to claim 6, in which the spray of solvent is under pressure of approximately thrity to ninety pounds per square inch, and the rinse water is under pressure of at least approximately 300 pounds per square inch.

8. The method of removing from the interior of an integral fuel tank of an aircraft sealant that is adhering thereto, which consists in applying a pressure spray of solvent, which is adapted to remove said sealant, against at least the upper portions of the sealant to remove same and create a continuous downward flow in the tank of solvent and pieces of said removed sealant, simultaneously gravitationally draining removed particles of sealant out of the tank with said solvent, thereafter removing pieces of sealant in said flow by passing the flow through screening means, and

finally returning said residual solvent under pressure to the tank as the spray above mentioned;

KEITH R. WI-IITCOMB. EUGENE E. FINCH.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Re. 19,374 Butterworth Nov. 20, 1934 1,141,243 Foster June 1, 1915 1,628,141 Gray May 10, 1927 1,892,950 Houpt Jan. 3, 1933 2,092,321 McFadden Sept. '7, 1937 2,123,434 Paulson et al. July 12, 1938 2,442,272 Jafla May 25, 1953 2,458,333 Brady Jan. 4, 1949 

1. THE METHOD OF REMOVING THE SEALANT FROM AN AIRCRAFT INTEGRAL FUEL TANK THAT COMPRISES IMPINGING A SPRAY OF VOLATILE SOLVENT AGAINST AT LEAST THE UPPER PORTIONS OF THE SEALANT OF THE TANK WHILE THE LATTER IS SEALED, SIMULTANEOUSLY GRAVITATIONALLY DRAINING FREE SOLVENT FROM THE TANK WITH 